On Tue, Apr 16, 2024 at 04:08:21PM +0200, Benjamin Tissoires wrote:
> Introduce support for KF_ARG_PTR_TO_WORKQUEUE. The kfuncs will use bpf_wq
> as argument and that will be recognized as workqueue argument by verifier.
> bpf_wq_kern casting can happen inside kfunc, but using bpf_wq in
> argument makes life easier for users who work with non-kern type in BPF
> progs.
>
> Duplicate process_timer_func into process_wq_func.
> meta argument is only needed to ensure bpf_wq_init's workqueue and map
> arguments are coming from the same map (map_uid logic is necessary for
> correct inner-map handling), so also amend check_kfunc_args() to
> match what helpers functions check is doing.
>
> Signed-off-by: Benjamin Tissoires <bentiss@xxxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 86 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index deaf2e1ab690..112faf2cd7e9 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -332,6 +332,10 @@ struct bpf_kfunc_call_arg_meta {
> u8 spi;
> u8 frameno;
> } iter;
> + struct {
> + struct bpf_map *ptr;
> + int uid;
> + } map;
> u64 mem_size;
> };
>
> @@ -7598,6 +7602,43 @@ static int process_timer_func(struct bpf_verifier_env *env, int regno,
> return 0;
> }
>
> +static int process_wq_func(struct bpf_verifier_env *env, int regno,
> + struct bpf_kfunc_call_arg_meta *meta)
> +{
> + struct bpf_reg_state *regs = cur_regs(env), *reg = ®s[regno];
> + bool is_const = tnum_is_const(reg->var_off);
> + struct bpf_map *map = reg->map_ptr;
> + u64 val = reg->var_off.value;
> +
> + if (!is_const) {
> + verbose(env,
> + "R%d doesn't have constant offset. bpf_wq has to be at the constant offset\n",
> + regno);
> + return -EINVAL;
> + }
This check is unnecessary.
Before calling into this function it goes as:
switch (kf_arg_type) {
case KF_ARG_PTR_TO_MAP:
... your new checks ...
fallthrough;
case KF_ARG_PTR_TO_CTX:
arg_type |= OBJ_RELEASE;
break;
check_func_arg_reg_off()
if (arg_type_is_release(arg_type)
return __check_ptr_off_reg()
// that does offset checks
> + if (!map->btf) {
> + verbose(env, "map '%s' has to have BTF in order to use bpf_wq\n",
> + map->name);
> + return -EINVAL;
> + }
> + if (!btf_record_has_field(map->record, BPF_WORKQUEUE)) {
> + verbose(env, "map '%s' has no valid bpf_wq\n", map->name);
> + return -EINVAL;
> + }
above two are also unnecessary. wq_off will be negative otherwise.
> + if (map->record->wq_off != val + reg->off) {
> + verbose(env, "off %lld doesn't point to 'struct bpf_wq' that is at %d\n",
> + val + reg->off, map->record->wq_off);
> + return -EINVAL;
> + }
only this one is needed, but I need to study the rest of the patches.
> + if (meta->map.ptr) {
> + verbose(env, "verifier bug. Two map pointers in a workqueue helper\n");
> + return -EFAULT;
> + }
this was checked already as well.
> + meta->map.uid = reg->map_uid;
> + meta->map.ptr = map;
> + return 0;
> +}
> +
> static int process_kptr_func(struct bpf_verifier_env *env, int regno,
> struct bpf_call_arg_meta *meta)
> {
> @@ -10843,6 +10884,7 @@ enum {
> KF_ARG_LIST_NODE_ID,
> KF_ARG_RB_ROOT_ID,
> KF_ARG_RB_NODE_ID,
> + KF_ARG_WORKQUEUE_ID,
> };
>
> BTF_ID_LIST(kf_arg_btf_ids)
> @@ -10851,6 +10893,7 @@ BTF_ID(struct, bpf_list_head)
> BTF_ID(struct, bpf_list_node)
> BTF_ID(struct, bpf_rb_root)
> BTF_ID(struct, bpf_rb_node)
> +BTF_ID(struct, bpf_wq)
>
> static bool __is_kfunc_ptr_arg_type(const struct btf *btf,
> const struct btf_param *arg, int type)
> @@ -10894,6 +10937,11 @@ static bool is_kfunc_arg_rbtree_node(const struct btf *btf, const struct btf_par
> return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_RB_NODE_ID);
> }
>
> +static bool is_kfunc_arg_wq(const struct btf *btf, const struct btf_param *arg)
> +{
> + return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_WORKQUEUE_ID);
> +}
> +
> static bool is_kfunc_arg_callback(struct bpf_verifier_env *env, const struct btf *btf,
> const struct btf_param *arg)
> {
> @@ -10963,6 +11011,7 @@ enum kfunc_ptr_arg_type {
> KF_ARG_PTR_TO_NULL,
> KF_ARG_PTR_TO_CONST_STR,
> KF_ARG_PTR_TO_MAP,
> + KF_ARG_PTR_TO_WORKQUEUE,
> };
>
> enum special_kfunc_type {
> @@ -11119,6 +11168,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
> if (is_kfunc_arg_map(meta->btf, &args[argno]))
> return KF_ARG_PTR_TO_MAP;
>
> + if (is_kfunc_arg_wq(meta->btf, &args[argno]))
> + return KF_ARG_PTR_TO_WORKQUEUE;
> +
> if ((base_type(reg->type) == PTR_TO_BTF_ID || reg2btf_ids[base_type(reg->type)])) {
> if (!btf_type_is_struct(ref_t)) {
> verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",
> @@ -11720,6 +11772,30 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
> case KF_ARG_PTR_TO_NULL:
> continue;
> case KF_ARG_PTR_TO_MAP:
> + if (meta->map.ptr) {
> + /* Use map_uid (which is unique id of inner map) to reject:
> + * inner_map1 = bpf_map_lookup_elem(outer_map, key1)
> + * inner_map2 = bpf_map_lookup_elem(outer_map, key2)
> + * if (inner_map1 && inner_map2) {
> + * timer = bpf_map_lookup_elem(inner_map1);
> + * if (timer)
> + * // mismatch would have been allowed
> + * bpf_timer_init(timer, inner_map2);
adjust the comment too. Here it can only be wq.
> + * }
> + *
> + * Comparing map_ptr is enough to distinguish normal and outer maps.
> + */
> + if (meta->map.ptr != reg->map_ptr ||
> + meta->map.uid != reg->map_uid) {
let's also gate this check with map->record->wq_off.
Otherwise it will trigger for maps that don't have wq field.
Copy paste is a bit unfortunate, but fine. We can clean it up later.
> + verbose(env,
> + "workqueue pointer in R1 map_uid=%d doesn't match map pointer in R2 map_uid=%d\n",
> + meta->map.uid, reg->map_uid);
> + return -EINVAL;
> + }
> + }
> + meta->map.ptr = reg->map_ptr;
> + meta->map.uid = reg->map_uid;
> + fallthrough;
> case KF_ARG_PTR_TO_ALLOC_BTF_ID:
> case KF_ARG_PTR_TO_BTF_ID:
> if (!is_kfunc_trusted_args(meta) && !is_kfunc_rcu(meta))
> @@ -11752,6 +11828,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
> case KF_ARG_PTR_TO_CALLBACK:
> case KF_ARG_PTR_TO_REFCOUNTED_KPTR:
> case KF_ARG_PTR_TO_CONST_STR:
> + case KF_ARG_PTR_TO_WORKQUEUE:
> /* Trusted by default */
> break;
> default:
> @@ -12038,6 +12115,15 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
> if (ret)
> return ret;
> break;
> + case KF_ARG_PTR_TO_WORKQUEUE:
> + if (reg->type != PTR_TO_MAP_VALUE) {
> + verbose(env, "arg#%d doesn't point to a map value\n", i);
> + return -EINVAL;
> + }
> + ret = process_wq_func(env, regno, meta);
> + if (ret < 0)
> + return ret;
> + break;
> }
> }
>
>
> --
> 2.44.0
>
